Re: Audigy DSP questions.

[James Courtier-Dutton <James@superbug.co.uk>]

James Courtier-Dutton wrote:
> In emufx.c there is the following table. Can anyone tell me how to 
> convert these values to floating point db gain values?
> I need to know how to convert values in the DSP to values in the range 
> +2.0 to -2.0
> 
> static const u32 db_table[101] = {
>         0x00000000, 0x01571f82, 0x01674b41, 0x01783a1b, 0x0189f540,
>         0x019c8651, 0x01aff763, 0x01c45306, 0x01d9a446, 0x01eff6b8,
>         0x0207567a, 0x021fd03d, 0x0239714c, 0x02544792, 0x027061a1,
>         0x028dcebb, 0x02ac9edc, 0x02cce2bf, 0x02eeabe8, 0x03120cb0,
>         0x0337184e, 0x035de2df, 0x03868173, 0x03b10a18, 0x03dd93e9,
>         0x040c3713, 0x043d0cea, 0x04702ff3, 0x04a5bbf2, 0x04ddcdfb,
>         0x0518847f, 0x0555ff62, 0x05966005, 0x05d9c95d, 0x06206005,
>         0x066a4a52, 0x06b7b067, 0x0708bc4c, 0x075d9a01, 0x07b6779d,
>         0x08138561, 0x0874f5d5, 0x08dafde1, 0x0945d4ed, 0x09b5b4fd,
>         0x0a2adad1, 0x0aa58605, 0x0b25f936, 0x0bac7a24, 0x0c3951d8,
>         0x0ccccccc, 0x0d673b17, 0x0e08f093, 0x0eb24510, 0x0f639481,
>         0x101d3f2d, 0x10dfa9e6, 0x11ab3e3f, 0x12806ac3, 0x135fa333,
>         0x144960c5, 0x153e2266, 0x163e6cfe, 0x174acbb7, 0x1863d04d,
>         0x198a1357, 0x1abe349f, 0x1c00db77, 0x1d52b712, 0x1eb47ee6,
>         0x2026f30f, 0x21aadcb6, 0x23410e7e, 0x24ea64f9, 0x26a7c71d,
>         0x287a26c4, 0x2a62812c, 0x2c61df84, 0x2e795779, 0x30aa0bcf,
>         0x32f52cfe, 0x355bf9d8, 0x37dfc033, 0x3a81dda4, 0x3d43c038,
>         0x4026e73c, 0x432ce40f, 0x46575af8, 0x49a8040f, 0x4d20ac2a,
>         0x50c335d3, 0x54919a57, 0x588dead1, 0x5cba514a, 0x611911ea,
>         0x65ac8c2f, 0x6a773c39, 0x6f7bbc23, 0x74bcc56c, 0x7a3d3272,
>         0x7fffffff,
> };
> 
> 

I think I have worked it out.
Take each value and divide by 0x80000000 to get a value between 0 and 1.
This is then converted into dB with
0 == Mute
0x01571f82 == -19.8 dB
0x7fffffff == 0 dB
With each value being a constant step of 0.2 dB.

James


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